On Thursday, a 16-year-old boy dancing on the top of an open roof double-decker bus was struck by the concrete overpass, as the bus drove down the 405 freeway in Inglewood, CBS News reports.

According to a witness, the boy may have been standing on a seat cushion with his back to the freeway, when he was slammed in the head and then collapsed on the floor. At the time of the accident, according to NBC 4, about two dozen teenagers were dancing on the open top deck. Notably, the bus was accompanied by chaperones who were apparently inside the bus on the lower deck.

California Highway Patrol Officer Edgar Figueroa stated that the Starline Tours bus was traveling just before 8 p.m., near the Arbor Vitae Street overpass, when the incident occurred. The teen was taken to Harbor-UCLA Medical Center, where he is listed in critical condition.

So far, officials with Starline have not commented on the shocking incident, other than that alcohol is never served on their tour buses.